Qualitative and semi-quantitative physico-chemical characterization of some calcium phosphate implant and bone samples

Ten calcium phosphate implant substances (six of natural origin, four of synthetic origin) and several bone samples from a single human skeleton have been qualitatively and semi-quantitatively characterized with respect to several physico-chemical properties. Analysis involved the techniques of X-ray powder diffraction, infra-red spectroscopy, inductively-coupled plasma atomic emission spectroscopy, atomic absorption spectroscopy, and thermal decomposition. In addition, a series of adsorption/exchange experiments were conducted in which implant and bone samples were exposed to progressively increasing concentrations of aqueous Ca²⁺ and Na⁺ ions. X-ray powder diffraction showed that the implants consist of only hydroxyapatite while bones contain small amounts of CaO as well. a-Cell parameters of the implants of natural origin were larger than those of both synthetic implants and bones. The a-cell sizes of the latter two types of samples resembled each other. The c-cell sizes were similar for all samples. The degrees of crystallinity of all implants were higher than those of bone, possibly indicating lower CO₃ contents in the former. %Mass contents of various elements were determined by ICP for implants and bones. Statistical analysis on the bone values showed that variation of elemental concentrations not attributable to experimental error occurred in bone from different regions of the body, but not across the surface of any particular bone. Ratios of Ca/P and Mg/Ca were calculated for all samples, and showed differences between implants and bone due to higher calcium levels in the former. Infrared spectroscopy was used in order to determine %CO₃ values in all the samples. It is suggested that bone contains higher levels of CO₃ than the implants. This was confirmed by analysis of the shapes of certain bands in the spectra of all samples and correlated with XRD results. All samples were subjected to heat up to a maximum of 900°C. XRD scans were recorded after heating to 650°C and 900°C. Percentage mass losses were also recorded at various stages throughout the heating process. Some of the implants revealed traces of tricalcium phosphate (β-TCP) and Cao after heating to 900°C. All bones revealed traces of CaO after heating to 900°C. a-Cell parameters were calculated for all samples and revealed very slight changes in size. Implants exhibited most of these changes after heating to 650°C, while bones did so only after heating to 900°C. Surface chemistry studies further confirmed chemical differences between implants and bone by virtue of the fact that neither exogenous Ca²⁺ nor Na⁺ adsorbed/exchanged with ions in the implants, while bone exhibited a clear saturation curve for each exogenous ion. It is suggested that the techniques and experiments described in this thesis might be utilized by other investigators in the hope of establishing guidelines for the selection of appropriate implant substances.

Reference:

Schindler, G. 1991. Qualitative and semi-quantitative physico-chemical characterization of some calcium phosphate implant and bone samples. University of Cape Town.